Biochemical and Microbial Biomarkers Mediating Feed Efficiency in Cattle

Beef cattle are the primary red meat consumed in the United States and provide greater than $105 billion in retail value each year. In the beef industry, feed represents approximately 60% of the total input costs. Thus, finding novel ways of improving feed efficiency in order to reduce that cost is imperative. This research assesses several aspects of the ruminal microbiome in relation to feed efficiency in steers, including stability of the ruminal bacteriome following transition to feed, serum metabolites in steers differing in feed efficiency, as well as potential microbial and biochemical biomarkers of feed efficiency. In this study,50 Black Angus steers of 7 months of age were acclimated to the GrowSafe© feeding system and fed a step-up receiving diet before receiving a growing ration. Steers were maintained on the diet for 70d. Weekly BW was measured, serum collected, and rumen content was obtained via gastric tubing. The average RFI was calculated and steers were divided into low- (n=14) and high-RFI (n=15) groups based on 0.5 SD below and above the mean RFI, respectively. Untargeted serum metabolomics was conducted utilizing LC-MS. Genomic DNA was extracted from rumen content and the amplified V1-V3 hypervariable region of the bacterial 16S rRNA gene was sequenced for analyses. Missing values were approximated through matrix completion and data was normalized using a centered log-ratio transformation. Random Forests supervised machine learning and feature selection was performed on the bacterial compositions. Ruminal bacteria diversityfluctuated over the course of the trial, and was lower at the end of the trial compared to the beginning (P<0.05). Low-RFI steers were associated with decreased bacterial α [alpha]-(P=0.03) and β-[beta] diversity (R²=1, P=0.001), and greater abundances of pantothenate (0.375; P=0.04) as well as reduced abundances of glucose-6-phosphate (2.13; P=0.02) and glucose-1-phosphate (2.13; P=0.03). Fold change Flavobacteriia abundances were greater with increased pantothenate contrasted to reduced pantothenate (5.06; P=0.04). Greater abundances of pantothenate-producing bacteria, such as Flavobacteriia, may result in improved nutrient utilization in low-RFI steers. Pantothenate and/or Flavobacteriia may serve as potentially novel biomarkers to assess or predict feed efficiency in Black Angus steers on a backgrounding diet.